SMU - SECTION 3B - CONTROL MODULE SYSTEM. GMC Truck Sonoma Pickup

SUBJECT: SERVICE MANUAL UPDATE-SECTION 3B-CONTROL MODULE SYSTEM (VCM-A) - REVISED DIAGNOSTIC AIDS

MODELS: 1995 CHEVROLET AND GMC TRUCK S/T MODELS WITH AUTOMATIC AND MANUAL TRANSMISSION AND 4.3L ENGINE (VIN W - RPO L35)

THIS BULLETIN IS BEING ISSUED TO REVERSE THE DIAGNOSTIC AIDS UNDER P0117, P1114 AND P0118, P1115. THIS IS IN THE 1995-S/T DRIVEABILITY, EMISSIONS AND ELECTRICAL DIAGNOSIS MANUAL # GMT/95-ST.

PAGES 3B-59, 3B-61 AND 3B-143, 3B-145 SHOULD READ AS FOLLOWS:

**P0117, P1114** CHECK HARNESS ROUTING FOR A POTENTIAL SHORT TO GROUND IN THE 5 VOLT REFERENCE CIRCUIT.

THE SCAN TOOL DISPLAYS ENGINE TEMPERATURE IN DEGREES CENTIGRADE. AFTER ENGINE IS STARTED, THE TEMPERATURE SHOULD RISE STEADILY TO ABOUT 90 DEGREES C, THEN STABILIZE WHEN THERMOSTAT OPENS.

THE "TEMPERATURE VS. RESISTANCE VALUE" SCALE MAY BE USED TO TEST THE COOLANT SENSOR AT VARIOUS TEMPERATURE LEVELS TO EVALUATE THE POSSIBILITY OF A "SKEWED" (MIS-SCALED) SENSOR. A "SKEWED" SENSOR COULD RESULT IN POOR DRIVEABILITY CONCERNS.

**P0118, P1115** A FAULTY CONNECTION OR AN OPEN IN THE 5 VOLT REFERENCE CIRCUIT OR THE SENSOR GROUND CIRCUIT WILL RESULT IN A DTC P0117.

THE SCAN TOOL DISPLAYS ENGINE TEMPERATURE IN DEGREES CENTIGRADE. AFTER ENGINE IS STARTED, THE TEMPERATURE SHOULD RISE STEADILY TO ABOUT 90 DEGREES C, THEN STABILIZED WHEN THERMOSTAT OPENS.

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GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.